Optical disks are known as reliable optical recording media capable of recording information in high density. Such optical disks are available in a single-sided type, that is, information may be recorded on one side of the disk and the information thus recorded may be reproduced, and in a double-sided type, that is information may be recorded on both sides of the disk and the information thus recorded may be reproduced. The latter optical disk is usually used, as rotatably housed in a cartridge case, for recording information and reproducing the information thus recorded.
Referring to FIGS. 6 and 7, an optical disk 31 of the double-sided type is provided at the center thereof with a clamping hub 32 for rotating the optical disk 31 through a rotary system of a drive mechanism (not shown). The optical disk 31 is rotatably housed in a case 33 provided in both lateral sides thereof with openings 34. The case 33 includes a first case member 33a and a second case member 33b. As shown in FIG. 7, a guide groove 35 is formed by guide walls 36a, 36b at the lateral sides of the case 33 and projections 37a, 37b respectively formed on the inner surfaces of the guide walls 36a, 36b. The guide groove 35 is formed at one end of the case 33.
A slider (not shown) is slidably disposed in the guide groove 35. A shutter 38 for covering the openings 34 of the case 33 is attached to the slider by attaching means such as screws 39 or the like. The slider is normally pushed in one direction by a spring (not shown) disposed in the case 33.
Formed in the slider and the shutter 38 at predetermined positions thereof are slots 41 with which two shutter opening pins (not shown) of the drive mechanism are adapted to be engaged. The shutter engaged with one of the opening pins is used for opening and closing the openings 34 of the case 33 in order that both sides of the optical disk 31 may be used for recording information and reproducing the information thus recorded. More specifically, when one side of the optical disk 31 is to be used, one opening pin is reciprocated to open and close the openings 34 by the shutter 38, and when the other side of the optical disk 31 is to be used, the case 33 is first reversed and the other opening pin reciprocates the shutter 38 to open and close the the openings 34 of the case 33.
The shutter 38 is provided at one end thereof with a turned piece 40 which is turned toward the inside of the guide groove 35. This turned piece 40 is formed such that, when one opening pin reciprocates the shutter 38 for opening and closing the openings 34 of the case 33, the other opening pin which is not being used for reciprocating the shutter 38, is smoothly guided along the inclined surface of the turned piece 40, thereby to prevent the other opening pin from being caught by the shutter 38.
The efficiency of properly moving away the opening pin which is not being used for reciprocating the shutter 38, depends on the width of the inclined surface of the turned piece 40. Accordingly, to smoothly move away the opening pin in the cartridge case above-mentioned, it is preferable to reduce the thicknesses of the guide walls 36a, 36b to increase the width of the turned piece 40. However, the reduction of the guide walls 36a, 36b in thickness results in reduced strength thereof. It is therefore difficult to reduce the thicknesses of the guide walls 36a, 36b to increase the width of the turned piece 40. Thus, it is inevitable to reduce the width of the turned piece 40. On the other hand, when the width of the inclined surface of the turned piece 40 is small, the opening pin which is not being used may be caught by the shutter 38 when the drive mechanism is driven. This may prevent the shutter 38 from being opened and closed.